NOAA/WDS Paleoclimatology - Brazil Margin 25,000 Year Benthic Foraminiferal B/Ca and Carbonate Data

Carbon isotope minima were a ubiquitous feature of the mid‐depth Atlantic during Heinrich Stadial 1 (HS1, 14.5-17.5 kyr BP) and the Younger Dryas (YD, 11.5-12.9 kyr BP), yet their cause remains unclear. Recent evidence indicates that North Atlantic processes triggered the d13C anomalies, with weakening of the Atlantic Meridional Overturning Circulation (AMOC) being the most likely driver. Model simulations suggest that slowing of the AMOC increases the residence time of mid‐depth waters in the Atlantic, resulting in the accumulation of respired carbon. Here we assess ECO2 variability in the South Atlantic using benthic foraminiferal B/Ca, a proxy for [CO32-]. Using replicated high‐resolution B/Ca records from ~2 km water depth on the Brazil Margin, we show that [CO32-] decreased during HS1 and the YD, synchronous with apparent weakening of the AMOC. The [CO32-] response is smaller than in the tropical North Atlantic during HS1, indicating there was a north-south gradient in the [CO32-] signal similar to that for d13C. The implied variability in ECO2 is consistent with model results, suggesting that carbon is temporarily sequestered in the mid‐depth Atlantic during millennial‐scale stadial events. Using a carbon isotope mass balance, we estimate that approximately 75% of the HS1 d13C signal at the Brazil Margin was driven by accumulation of remineralized carbon, highlighting the nonconservative behavior of d13C during the last deglaciation.